1. Field of the Invention
This invention relates to a hydraulic brake control assembly for vehicles and more particularly to a hydraulic brake inertia-controlled proportioning valve responsive to vehicle deceleration.
2. Description of the Prior Art
Conventionally, various hydraulic brake control assemblies for vehicles have been proposed which include proportioning valve means to thereby reduce the hydraulic pressure in the rear wheel brake cylinder with respect to the hydraulic pressure in the master cylinder after the hydraulic pressure in the master cylinder reaches a predetermined value (deflecting point). The proportioning valve means is well-known and comprises a piston having an enlarged valve portion which is engageable with a resilient seat member and a spring to bias the piston in a direction in which the valve portion is spaced from the seat member. In addition, it is well-known that it is desirable to actuate the proportioning valve means in accordance with vehicle loading, namely it is desirable to shift the deflecting point in accordance with vehicle loading. Therefore, prior hydraulic brake control assemblies further included means for modifying the biasing force of the spring which biases the piston of the proportioning valve means in accordance with the vehicle loading.
The means for modifying the biasing force of the spring comprises a plunger which is slidable by means of the hydraulic pressure in the master cylinder to thereby modify the biasing force of the spring, and an inertia-responsive ball for controlling admission of the hydraulic pressure to the plunger according to vehicle deceleration. In such prior assemblies, however, the pressure receiving area of the plunger is set to be larger than that of the piston and therefore the plunger may be moved so as to increase the biasing force of the spring before reaching the deflecting point, namely before the piston is initially moved. This means that the deflecting point may be undesirably raised especially when the vehicle loading is small and thus desirable control of the hydraulic brake pressure will not be obtained.
In order to obviate the above-noted disadvantage, prior brake control assemblies include a check valve which is positioned between the inertia-responsive ball and the plunger to thereby admit the hydraulic pressure to the plunger only after the hydraulic pressure reaches the predetermined value as disclosed for example in U.S. Pat. No. 3,944,293. In such prior assemblies, however, the construction thereof is complex in nature.